The present invention relates generally to printing presses and more particularly to a signature transfer device for transporting printed products.
A web printing press, for example for newspapers, will print a continuous web of material. In a folder of the printing press, the web will be folded, if desired, and then cut, so that signatures result. The signatures can then be conveyed on a conveyor and then transferred by a signature transfer device to another conveyor for further processing or delivery.
U.S. Pat. No. 4,482,141 discloses a method and device for conveying signatures from a blade chain conveyor supporting the signatures directly at a fold line. The signatures are gripped from above by orbitally-rotating clamping pads, which then transfer the signatures to a belt conveyor perpendicular to the blade chain conveyor. A tension spring forces the gripper fingers together. This patent is hereby incorporated by reference herein.
European Patent Application No. 0771 675 A1 discloses a device for removing signatures from a saddle conveyor supporting the signatures. The conveyor has cutouts that permit the signatures to be gripped from above by a rotating clamping device, which then further conveys the signatures to a belt conveyor.
U.S. patent application No. 2001/00327741 discloses a device for removing signatures from a saddle conveyor that moves the signatures over cutouts in a sword. Grippers grip the outside of the signature from above and transfer the signatures to a further conveying device.
An object of the present invention is to permit efficient removal of signatures and transfer from a conveyor.
The present invention provides a signature transfer device comprising: a rotating arm rotating about a first axis; a first gripper rotatably mounted on the rotating arm about a second axis, the first and second axes being parallel, the first gripper having a first gripper finger and a second gripper finger; an actuator connected to the first gripper for opening and closing the first gripper as a function of the angle of the rotating arm about the first axis; and a compression spring connecting the first gripper finger and the second gripper finger, the compression spring being compressed when the first gripper and the second gripper finger are apart.
By using a compression spring, various signature thicknesses can be accommodated without the need for control elements. As the signature thickness increases, the spring force increases since the compression spring is further compressed. Complicated signature thickness adjustments are not necessary. Preferably, the signature thicknesses range between 0 and 2.5 cm.
Preferably, the actuator is a cam follower interacting with a cam on the arm.
Preferably, the signature transfer device includes a second gripper rotating about the axis. The first and second grippers may be supported rotatably on a rotating arm rotating about the axis.
Preferably, the compression spring is compressed less than 10% of its uncompressed length when the first gripper finger and second gripper finger are closed without holding a signature. The spring can thus be changed without danger of the compression spring provided too much force during the changing operation.
The first gripper finger preferably includes a support rod extending through the second gripper finger, the support rod supporting the compression spring.
The first gripper preferably includes a support, the first and second gripper fingers and the cam follower being rotatable with respect to the support. The first and second gripper fingers may be geared together, and the cam follower may rotate one of the gears.
The support rod preferably has a removable nut at one end to support one end of the compression spring. The other end of the spring preferably is supported by the support, the spring thus being indirectly connected to the second gripper finger via the support.
The spring preferably extends through the rotating arm, and may be surrounded by the support. A first pulley may be fixed to an outer surface of the support, the support and the first pulley thus being rotatable with respect to the arm, which may house the support at a bearing surface.
The arm preferably is rotated via a central shaft. A fixed pulley preferably surrounds the central shaft, and is connected for example to a frame of a printing press or to the ground, so that the central shaft rotates with respect to the fixed pulley. A first belt preferably runs between the fixed pulley and the first pulley, so that as the arm rotates, the first belt causes the first gripper to maintain its orientation. A second pulley may be attached to the second gripper and, through a second belt, to the fixed pulley.
The present invention also provides a printing press comprising a print unit for printing a material, a conveyor for moving a plurality of signatures formed from the material in a first direction, and a signature transfer device for transferring signatures downstream of the conveyor. The signature transfer device has a rotating arm rotating about a first axis and a first gripper rotatably mounted on the rotating arm about a second axis, the first and second axes being parallel, the first gripper having a first gripper finger and a second gripper finger; an actuator connected to the first gripper for opening and closing the first gripper as a function of the angle of the rotating arm about the first axis; and a compression spring connecting the first gripper finger and the second gripper finger, the compression spring being compressed when the first gripper and the second gripper finger are apart.
Preferably, the printing press is a web printing press, and further includes a folder for forming signatures from the web.
A signature lifting device can be provided to lift the signatures from the conveyor, or the signatures can be transferred directly from the conveyor.
xe2x80x9cGripper fingerxe2x80x9d as defined herein is any gripper part used to contact a signature.